This invention relates to a method of predicting yarn caterpillar length.
Yarns such as polyamide or polyester are conventionally bulked for use in carpets and other end-use applications requiring bulky fibre by passing them through a set of hot rollers. The yarn is then contacted with an air jet to pull the yarn away from the rollers and impinge it upon a rotating drum. The rotating drum comprises an endless textured screen forming a cylindrical outer surface of the drum and a frame to support the screen. The yarn forms into a "caterpillar", which is a kinked or bunched formation, as soon as it contacts the screen, because there is no tension on the yarn. Air is exhausted from the centre of the drum to draw air through the screen and cool the yarn. The yarn is allowed to remain on the drum for about one-quarter of a rotation to adequately cool the yarn and is then pulled off of the drum using take-up rollers. The caterpillar length should be fairly constant to ensure that consistent bulking properties are achieved.
The term "caterpillar length" as used herein means the length of kinked or bunched yarn contacting the drum. This parameter is directly related to the length of time the yarn remains on the drum and so may be reported in terms of either length or time. In practice, the yarn may not remain on the drum for a sufficiently long period of time and so the yarn may not be cooled sufficiently. Moreover, caterpillar length may fluctuate widely, so that consistent yarn properties are not achieved.
It is desirable to predict caterpillar length changes to monitor the bulking properties of the yarn. It is also desirable to control caterpillar length changes to obtain or maintain optimal bulking properties.